JPS62262482A - semiconductor laser equipment - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] The present invention provides an external cavity type semiconductor in which two orthogonal polarized lights with two different frequencies are obtained by inserting a 174 wavelength plate in one of the external cavities and a birefringent material in the other. The laser device is unique.

[Industrial application field]

The present invention relates to a semiconductor laser device used as a dual-frequency light source, and particularly to an external cavity type semiconductor laser device that can reduce the number of component parts and can vary the frequency difference between two-frequency lights.

With the development of optical application technology, devices with new functions are being developed at a rapid pace. In the field of optical measurement, there is also a need for methods for measuring various physical quantities using laser light. In order to perform highly accurate measurements using one of these methods, the optical heterodyne method, it is necessary to stably obtain two closely spaced laser beams of one frequency. Furthermore, due to the demand for downsizing of measuring instruments, it is necessary to use semiconductor lasers in place of the conventionally used gas lasers.

[Prior Art] Recently, the number of optical measurement devices that apply laser light in measurement fields such as distance measurement and speed measurement has been increasing, but in order to efficiently perform such measurements using the optical heterogain method, it is necessary to establish a stable frequency difference. Zeem and He-Ne lasers using the 1n effect are often used as dual-frequency light sources.Also, as other light sources, birefringent materials are used in the resonator of gas lasers. There is an example of obtaining two-frequency light by inserting the
Vo1.5. Number 101964). Another method is to divide the laser beam into two and slightly shift the frequency of one using an acousto-optic element to obtain ZJFa wave light.

In addition, as a two-frequency laser light source using a semiconductor laser, 1
Although there are patent applications for external resonator structures previously filed by the present applicant, such as Japanese Patent Application No. 58-177233), none have been put to practical use yet.

[Problem that the invention seeks to solve]

When attempting to obtain two-frequency light with different polarization planes using a semiconductor laser, a large phase difference occurs between polarization modes due to the anisotropy of the propagation constant caused by the waveguide structure inside the semiconductor laser. Therefore, the effective cavity length differs greatly between polarization modes.

There has been a problem in that it is extremely difficult to simultaneously oscillate two lights with extremely close frequencies and different polarization modes. Furthermore, the same problem remains unsolved in semiconductor laser devices having an external cavity structure.

[Means for solving problems]

The present inventors have solved the problem caused by the internal structure of the semiconductor laser by eliminating laser oscillation caused by reflection at the end face of the semiconductor laser, and rotating the polarization plane of the feedback light from the reflecting mirror by 90 degrees in an external cavity configuration. As a result, in order to solve the above-mentioned problems, an external cavity type semiconductor laser device was developed in which at least a semiconductor laser (1) is located in the center and reflectors (3) are arranged on both sides of the semiconductor laser (1). And.

A 174 wavelength plate (4) is arranged in one optical path (21) so that its axial direction is 45 degrees with respect to the TEB optical plane (11) of the semiconductor laser placed at the center, and 2
2) A semiconductor laser device is provided which is characterized in that a birefringent material (5) is inserted therein to obtain two orthogonal polarized lights having different frequencies.

[Effect]

In the present invention, the anisotropy of the semiconductor laser can be canceled by a combination of a semiconductor laser and a 174-wave plate, and a semiconductor laser medium that is isotropic with respect to various polarization components can be realized. By inserting a birefringent material into the resonator, the effective resonator length changes for the two polarized lights.
A frequency light source can be realized.

[Example] FIG. 1 is an example diagram showing the overall configuration of a semiconductor laser device according to the present invention, and FIG. 3 is a diagram showing the rotation state of the polarization plane in the device shown in FIG. 1, FIG. 4 is a diagram showing the degree of variability of the oscillation frequency in the device shown in FIG.
1 (bl is an embodiment diagram of a semiconductor laser device in which a laser device is integrated as a modified example of the present invention.

In FIGS. 1 and 2, 1 is a semiconductor laser with anti-reflection films formed on both end faces for use as an active medium; 2
is a collimating microlens that makes the emitted light from a semiconductor laser parallel.

3 is a reflecting mirror for returning light to the laser, and 4 is a birefringence axis oriented at 45 degrees with respect to the TE polarized light Nil of the semiconductor laser 1. The rotation angle θ1 is 4 from the corresponding virtual line of the TE polarization plane 11.
5 degrees] 17 made of crystal etc. arranged at an angle
The 4-wave plate 5 has a birefringence axis azimuth of (45+α) degrees with respect to the TE polarization plane 11 of the semiconductor laser 1 [in the figure, the axis direction is indicated by an arrow 51; The rotation angle θ2 is 45 degrees + α degrees from the corresponding virtual line] 1 made of a birefringent material such as quartz arranged at an angle.
74 wave plate, 21 and 22 indicate the optical path within the resonator.

In addition, the α degree is in the range of Q”<α<45°, and 5°
~10' is appropriate.

In the semiconductor laser device configured in this way, the light in the optical path 21 emitted from the laser 1 to the (A) side is transmitted through the lens 2.
The light is collimated by , passes through the 174-wave plate 4 , is reflected by tJ13 , passes through the 174-wave plate 4 again, is focused by the lens 2 , and enters the inside of the laser 1 .

Similarly, the light in the optical path 22 emitted from the laser 1 to the (B) side is collimated by the lens 2 and is collimated by the 174 wavelength plate 5.
After passing through 113, it is reflected by 174 again.
The light passes through the wavelength plate 5, is focused by the lens 2, and enters the inside of the laser I.

Therefore, the light that is initially emitted from the laser 1 to the left as TE polarized light passes through the 174-wave plate 4 back and forth (twice) and is converted into 7M polarized light that is orthogonal to the TE polarized light. On the other hand, 7M polarized light is T
It is converted to E-polarized light.

At this time, dotted line a-- including laser 1 inside the resonator
In the part (A) on the left side of .a', the anisotropy regarding the plane of polarization is completely canceled out by the 174-wave plate 4 as it moves back and forth.

However, in the part CB) on the right side of the resonator, a 174 wavelength plate 5 made of a birefringent material whose axis direction is slightly shifted from 45 degrees is inserted in the optical path 22, so the effective resonator for two orthogonal polarized lights is The length can be slightly different.

The result is two slightly different orthogonal polarizations TE with one frequency.
, TM will oscillate.

At this time, if the axial direction of the 174-wave plate 5 placed in the optical path 22 is (45+α) degrees, the directions of the two linearly polarized lights TE and TM that emit one oscillation are as shown in FIG.
When it is rotated by an angle α from the axis and the resonator length is 20 cm, the oscillation frequency difference between the two polarized lights changes linearly according to the rotation angle α, as shown in FIG.

In addition, in this embodiment, a 174 wavelength plate 4 is provided in the optical path 21.
Although the explanation has been made on the case where a polarization plane conversion effect is inserted, this does not in any way impede the use of an electro-optic effect element having a similar polarization plane conversion effect, for example.

In addition, as the 174-wave plate 5, a quarter-wave plate with an axial direction slightly shifted from 45 degrees was used in the above embodiment, but this has an axial direction of 45 degrees, which is the same as that of the quarter-wave plate 4, and its thickness is For example, a 178-wavelength plate may provide the same function.

FIG. 5 (al) is a side view and a sectional view of a semiconductor laser device according to the present invention in which optical elements are integrated.

This is because the substrate 7 on which the laser 1 is mounted is formed of a birefringent material such as crystal, and the surface of the substrate 7 has a recess 71 in which the laser 1 is embedded, and reflective mirrors 74 and 75 are formed on both end surfaces of the recess 71. The base Fi7 is mounted on a heat sink substrate 8 to construct an external cavity type semiconductor laser device.

At this time, the recess 71 is connected to the laser 1 and the reflecting mirror 74 on the substrate 7.
The region 72 between the laser 1 and the reflecting mirror 75 is formed on the surface of the substrate 7 so that the region 73 between the laser 1 and the reflecting mirror 75 has different thickness dimensions (corresponding to the length between the laser 1 and the reflecting mirror 74 or 75). The optical axis in the cross section of the regions 72 and 73 is oriented 4 degrees with respect to the TE polarization plane of the laser 1, as shown by the arrow 76.
It is 5 degrees.

Due to such a difference in thickness, the region 72 has the same function as the 174-wave plate 4, and the region 73 has a tilted axis.
/41fL It performs the same function as the long plate 5.

At this time, the length ■ of the region 72 is determined by the following equation.

m·λ/4 I= (m: odd number) no is the refractive index of the substrate 7 for ordinary rays, and ne is the refractive index of the substrate 7 for extraordinary rays.

Furthermore, the length of the region 73 can be changed according to the required frequency difference within a range that does not satisfy the above equation 1.

〔Effect of the invention〕

As explained above, according to the present invention, not only can a dual-frequency light source be easily realized using a semiconductor laser, but also the dual-frequency light source can be easily realized using a semiconductor laser.
The frequency difference between the frequencies becomes variable.

The effect of contributing to expanding the scope of application of heterogain measurement using light is remarkable.

[Brief explanation of drawings]

FIG. 1 shows a semiconductor laser according to one embodiment of the present invention! FIG. 1 is a diagram showing the overall configuration of the device. FIG. 2 is a perspective view of a portion of FIG. 1 according to the present invention. FIG. 3 is a diagram showing the rotation of the plane of polarization with respect to the set angle α of the quarter-wave plate 5. FIG. 4 is a diagram showing changes in the frequency difference between two-frequency lights with respect to the setting angle α of the 174-wave plate 5 when the resonator length is 20 cm. FIG. 5 (b) is a side view and a sectional view showing a semiconductor laser device in which optical elements are integrated according to another embodiment of the present invention. [Explanation of symbols] In these figures, 1 is a semiconductor with a non-reflective film, 3,
74 and 75 are reflecting mirrors, 4 is a left 1/4 wavelength plate, 5 is a right 174 wavelength plate, 7 is a substrate, and 72 and 73 are polarization propagation regions of the substrate 7 having different polarization plane conversion effects.

Claims (5)

[Claims] (1) An external cavity type semiconductor laser device in which reflective mirrors (3) are arranged on both sides of at least a semiconductor laser (1), and a quarter-wave plate (4) in one optical path (21). ) is arranged so that its axial direction is 45 degrees with respect to the TE polarization plane (11) of the semiconductor laser placed at the center, and a birefringent material (5) is placed in the optical path (22) on the other side. A semiconductor laser device characterized in that the laser beam is inserted to obtain two orthogonal polarized lights with different frequencies. (2) In claim 1 above, the birefringent material (5) is a quarter-wave plate, and its axial direction is slightly deviated from 45 degrees with respect to the TE polarization plane of the semiconductor laser. A semiconductor laser device characterized by: (3) The semiconductor laser device according to claim 1, wherein the birefringent material (5) is a wavelength plate having a thickness different from that of the quarter-wave plate (4). (4) The semiconductor laser device according to claim 3, wherein the birefringent material (5) is a 1/8 wavelength plate. (5) In claim 1 above, the birefringent material (5) is a substrate on which the semiconductor laser (1) is mounted (
7), the semiconductor laser (1) is embedded in a recess (71) formed on the surface of the substrate (7), and reflective mirrors (74) and (75) are provided on both end faces thereof. An external cavity type semiconductor laser device is configured, and the recess (71) is located between the region (72) in the substrate (7) between the semiconductor laser (1) and the reflecting mirror (74), and the semiconductor laser device. The laser (1) and the reflecting mirror (7
5) A semiconductor laser device characterized in that the semiconductor laser device is formed on the substrate (7) so that the regions (73) therebetween have mutually different thickness dimensions.